[low-power] implement forward tracking series (#5608)

This commit implements the Forward Tracking Series feature in Link Metrics.

- Two new apis are added:
  - otLinkMetricsSendMgmtRequestForwardTrackingSeries, which is used
    to send an MLE Link Metrics Management Request
  - otLinkMetricsSendLinkProbe, which is used to send an MLE Link Probe

- A new class LinkMetricsSeriesInfo is used to maintain the data of
  one Series configured by a neighbor. This class inherits
  LinkedListEntry and each Neighbor has a list of
  LinkMetricsSeriesInfo. All LinkedListEntrys are allocated and freed
  by a Pool in LinkMetrics.

- To specify SeriesFlags in cli command for Forward Tracking Series, a
  similar approach with LinkMetricsFlags is used. Another character
  flags is used to represent SeriesFlags.

- Whenever the node receives a frame (including ACK) from a neighbor,
  it would call Neighbor::AggregateLinkMetrics which goes through each
  LinkMetricsSeriesInfo entry in the neighbor's list and aggregate the
  data if the frame type matches the entry.

- Two test scripts are added to test this function:
  - v1_2_LowPower_7_2_01_ForwardTrackingSeries.py
  - v1_2_LowPower_test_forward_tracking_series.py

tests/scripts/thread-cert/mle.py

@@ -58,6 +58,9 @@ class CommandType(IntEnum):
     ANNOUNCE = 15
     DISCOVERY_REQUEST = 16
     DISCOVERY_RESPONSE = 17
+    LINK_METRICS_MANAGEMENT_REQUEST = 18
+    LINK_METRICS_MANAGEMENT_RESPONSE = 19
+    LINK_PROBE = 20
     TIME_SYNC = 99
 
 
@@ -90,11 +93,22 @@ class TlvType(IntEnum):
     CSL_CHANNEL = 80
     CSL_SYNCHRONIZED_TIMEOUT = 85
     LINK_METRICS_QUERY = 87
+    LINK_METRICS_MANAGEMENT = 88
     LINK_METRICS_REPORT = 89
+    LINK_PROBE = 90
     TIME_REQUEST = 252
     TIME_PARAMETER = 253
 
 
+class LinkMetricsSubTlvType(IntEnum):
+    LINK_METRICS_REPORT = 0
+    LINK_METRICS_QUERY_ID = 1
+    LINK_METRICS_QUERY_OPTIONS = 2
+    FORWARD_PROBING_REGISTRATION = 3
+    LINK_METRICS_STATUS = 5
+    ENHANCED_ACK_LINK_METRICS_CONFIGURATION = 7
+
+
 class SourceAddress(object):
 
     def __init__(self, address):
@@ -1117,6 +1131,19 @@ class LinkMetricsQueryFactory:
         return LinkMetricsQuery()
 
 
+class LinkMetricsManagement:
+    # TODO: Not implemented yet
+
+    def __init__(self):
+        print("LinkMetricsManagement is not implemented yet.")
+
+
+class LinkMetricsManagementFactory:
+
+    def parse(self, data, message_info):
+        return LinkMetricsManagement()
+
+
 class LinkMetricsReport:
     # TODO: Not implemented yet
 
@@ -1130,6 +1157,19 @@ class LinkMetricsReportFactory:
         return LinkMetricsReport()
 
 
+class LinkProbe:
+    # TODO: Not implemented yet
+
+    def __init__(self):
+        print("LinkProbe is not implemented yet.")
+
+
+class LinkProbeFactory:
+
+    def parse(self, data, message_info):
+        return LinkProbe()
+
+
 class MleCommand(object):
 
     def __init__(self, _type, tlvs):